In the case of an air conditioner constituting a refrigerant circuit, in general, the air conditioner includes each unit of an indoor unit and an outdoor unit and a pipeline that connects therebetween. As the configuration of the units, the indoor unit has an indoor-side heat exchanger, and the outdoor unit has an outdoor-side heat exchanger, a compressor, and a decompression device, which are connected to one another by the pipeline within the unit. The units formed thereby are connected by piping on an installation site and function as an air conditioner.
The inside of the refrigerant circuit formed by connecting the above units is filled with a refrigerant in general, and moreover, refrigerating machine oil that drives the compressor is also present in the refrigerant circuit. In general, if the outside temperature is low and the temperature inside the compressor is lower than the outside temperature and there is a temperature difference between the outside temperature and the temperature inside the compressor, a phenomenon in which the refrigerant collects in the compressor of the outdoor unit whose temperature becomes low, occurs. If the refrigerant collects in the compressor, the refrigerating machine oil is diluted by the refrigerant or liquefied refrigerant is left in a compressor chamber. If the compressor is started in this state, the refrigerating machine oil is discharged with the refrigerant, which results in a shortage of the refrigerating machine oil in the compressor, and compression of the collected liquid refrigerant increases a compressor load. Both of the factors cause failure in the compressor.
Thus, in order to avoid the above phenomenon, means that suppresses collection of the refrigerant while the air conditioner is stopped has been used in a compressor of an air conditioner in general by supplying electricity to a device for heating a shell (heater) or a motor in the compressor so as to heat the compressor. The timing at which this means is operated is determined using a predetermined outside temperature as a trigger, and a control technology of heating the compressor has been provided if the outside temperature is lower than the predetermined temperature or during the night when the outside temperature is lower than the predetermined temperature (See Patent Document 1).
Also, a control technology of starting supply of electricity to a shell heating device (crankcase heater) if a detected temperature of a shell temperature sensor falls under a detected value of every temperature detecting device in the air conditioner has been provided (See Patent Document 2).